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Title: Structural Uncertainty Analysis of Nuclear Reactor Core Load Pads
Creator: Wozniak, Nicholas
Date: 2019
Description: In fast spectrum nuclear reactors, reactivity is directly related to the capability of the reactor to sustain a fission chain reaction for...
Show moreIn fast spectrum nuclear reactors, reactivity is directly related to the capability of the reactor to sustain a fission chain reaction for power production. Historically, mechanical/structural analysis and design have been driven primarily by deterministic methods. However, reactivity is extremely sensitive to the location of the fuel within the reactor; which is subject to uncertainties. This makes deterministic models unstable and can allow manufacturing errors to contribute to uncertainties in analysis, resulting in potential safety concerns and incorrect reactor lifetime prediction. One potential means to address this challenge is the use of stochastic analysis. A framework is presented which introduces uncertainty analysis through the use of Monte Carlo Simulation. Latin Hypercube Sampling is used to reduce the number of sample runs and the computational effort and storage space requirements for the results. Geometric parameters such as the gaps at the load pad contact points, the location of the above core load pad (ACLP), and even temperature gradient profiles, that are important to the design of nuclear reactors are varied, and their effects on the overall performance are studied through sensitivity analysis. The main focus was to quantify the effects of the variation of these parameters directly on the variation of the contact forces and deformations of the fuel assemblies which house and control the movement of the fuel. Based on the results of the sensitivity study, this study found that the ACLP location has the largest effect on contact forces. And as such, any uncertainty in this parameter results in a rather large variation in the intensity of the contact force. Furthermore, specific recommendations are given to help control these variations as well as for further investigations on other parameters that may be significant to the design of fuel assemblies.
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Title: Structural Condition Assessment for Wind Turbine Towers
Creator: Zahraee, Afshin
Date: 2019
Description: Wind-based energy generation has special priority in efforts related to global sustainability. Based on this priority and the desire for...
Show moreWind-based energy generation has special priority in efforts related to global sustainability. Based on this priority and the desire for increase in electricity generation, the size of wind turbines has been tremendously increased in recent years. Moreover, larger wind turbines have access to more stable wind speeds which assists in electricity generation consistency. However, larger wind turbines are more prone to exhibit structural failure due to the increase of size as well as presence of complexities in the structure and wind load interaction. As such, condition monitoring and fault diagnosis of wind turbines are crucial in their sustainable operation. In this work, a new framework for condition assessment of wind turbine towers is developed. This framework enhances the ability to assess the structural condition of in-service wind turbine towers. Using this framework: 1) the wind data for the wind turbine location is collected, 2) a series of numerical modeling and analysis for the wind turbine tower for various wind velocities are performed to obtain the maximum induced stresses and their corresponding critical fatigue components (hot spots), and 3) fatigue analysis is performed leading to prediction for the remaining life of the wind turbine tower. To illustrate the capability of the present method, a case study is performed on an existing wind turbine. The obtained analytical results are compared and verified by the original design parameters. The results obtained for life prediction of the wind turbine tower correlate with life predictions of other existing wind turbine towers. It is anticipated that application of this framework for existing and future wind turbines will enhance their inspection planning as well as offer a more cost-effective process for repair and rehabilitation of wind turbine towers. This will ultimately increase the overall safety of wind turbine systems and enhance their reliability of performance.Keywords: Wind Turbine Tower, Condition Assessment, Life Prediction.
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Title: MODELING THE ORIGIN AND INCEPTION OF FATIGUE FAILURE IN METALS THROUGH A NON-LINEAR MECHANICAL SPRING SYSTEM
Creator: Divani, Abbas
Date: 2019
Description: Fatigue failure of metals is one of the aspects of material behavior that have not been explained through direct calculations or mathematical...
Show moreFatigue failure of metals is one of the aspects of material behavior that have not been explained through direct calculations or mathematical modeling. This research is to undertake the development of an innovative model that can be used in predicting the fatigue behavior of metals. This model is based on the behavior of a system of large number of parallel elements, each composed of two springs, a string, and a mass block, that undergo cyclically varying or random load cycles. Failures among the elements occur at random and can be used as a means to simulate fatigue damage and fatigue behavior. Initial studies on this model have produced promising results. This research is intended for full development and implementation of the model including procedures for Development of a method for calibration of the model parameters using the common mechanical properties of steel, extension of the model to incorporate the hysteresis behavior of steel under cycling loading, and development of Constant Fatigue Life diagrams Such as Goodman diagram.
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Title: WIM BASED LIVE LOAD FACTORS FOR CONSISTENT ILLINOIS BRIDGE RELIABILITY
Creator: Chi, Jingya
Date: 2019
Description: The Load and Resistance Factor Rating (LRFR) approach was developed in the early 2000s. The live-load factors were calibrated at that time so...
Show moreThe Load and Resistance Factor Rating (LRFR) approach was developed in the early 2000s. The live-load factors were calibrated at that time so that bridges rated by the LRFR approach could achieve a uniform structural reliability. However, the first calibration of the live-load factors was intent on the applications to the entire nation, without considering state-specific traffic conditions and truck restrictions. In addition, the calibration was carried out using limited data collected from the weigh stations of Ontario, Canada, in the 1970s. Therefore, to develop a practice that is consistent with the current LRFR approach as well as considering the state-specific live-load effects has motivated us to conduct this study.We study the weigh-in-motion (WIM) data that have been collected by the Department of Transportation of several states (i.e., Michigan, New York, Minnesota, California, Illinois, Oregon, Kentucky and Pennsylvania). These data contain approximate four years (i.e., from 2013 to 2017) of continuously-recorded trucks. They provide the information about truck weight and configuration, as well as the truck traffic pattern. In this research, we focus on the data collected by the Illinois DOT to calibrate live-load factors for the Illinois LRFR highway bridge evaluation.We first propose and verify a simulation method to statistically restore the missing trucks in the second lanes in the Illinois data. Based on the concept of relative calibration, we propose 3 sets of live-load factors for the Illinois legal, routine permit and special permit load ratings. Then we conduct a sensitivity analysis on the overweight trucks. Finally, we study the effect of law enforcement on the calibration.
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Title: MULTI-OBJECTIVE OPTIMIZATION FOR LEED - NEW CONSTRUCTION USING GENETIC ALGORITHMS
Creator: ALOTHAIMEEN, IBRAHEEM
Date: 2018
Description: In the U.S., the building sector is responsible for 73% of electricity usage, 38% of CO2 emissions, and 13.6% of potable water. These data...
Show moreIn the U.S., the building sector is responsible for 73% of electricity usage, 38% of CO2 emissions, and 13.6% of potable water. These data indicate that the construction industry negatively impacts the global environment and natural resources. The concept of “sustainability” was introduced to set guidelines for the construction industry to limit its negative environmental impact. To promote sustainability in the construction industry, many organizations have introduced guidelines and rating systems for buildings. One of these rating systems is Leadership in Energy and Environmental Design (LEED) which is the most globally acknowledged system.Although LEED excels in reducing the negative environmental impacts and the energy consumption of buildings, the high costs in the early phases associated with the implementation and pursuit of LEED certification are pushing away some project owners from entering the process. Therefore, to balance these objectives in sustainable projects, an approach which optimizes multiple objectives is needed. In this study, a multi-objective optimization framework, which uses Non-dominated Sorting Genetic Algorithm-II (NSGA-II), is proposed to find the optimal solution in terms of life-cycle cost and sustainability for a new construction project pursuing LEED v4 BD+C certification. A BIM project of a 3-floor educational building was selected as a case study in the research. The study case is used to verify the efficiency and soundness of the proposed model. The results show that the method does indeed lead to optimal solutions.
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Title: NUMERICAL STUDY OF MICRO, MESO, AND MACRO-MECHANICAL BEHAVIOR OF COHESIONLESS GRANULAR MATERIALS USING 3D DEM ROLLING/TWISTING RESISTANCE MODELS
Creator: Goudarzi, Nima
Date: 2018
Description: It has been frequently demonstrated that the mechanical behavior of cohesionlessgranular materials including sand and gravel is significantly...
Show moreIt has been frequently demonstrated that the mechanical behavior of cohesionlessgranular materials including sand and gravel is significantly influenced by theirmorphological features including the shape and surface texture. Therefore, the primaryobjective of this thesis is to take a more critical look at micro-, meso- and macromechanicalbehaviors of cohesionless granular materials in response to effective modelingof the grains morphology and to establish a practical yet straightforward causal relationshipbetween micro-scale modeling and macro-scale soil behavior.To precisely investigate the effects of morphology on the macroscopic behavior, aparticle-based microscopic approach using the Discrete Element Method (DEM) wasemployed. In this regard, a novel 3D micro-mechanical contact model, based on the MTL(moment transfer law) theory, incorporating both rolling and twisting resistances, waspicked to describe the inter granular behavior between cohesionless particles. Severaltriaxial and direct shear tests were run to characterize link (s), if any, between the microscalefeatures and the macroscopic soil responses. Results from these tests were analyzedat both the peak and critical state. Through the development of a comprehensive calibrationmethodology and finding a reasonable match between numerical and experimental results,it was found that even in the ideal case of perfectly spherical grains, it is still possible toeffectively model the presence and effects of influential micro-scale morphologicalfeatures without the need for direct modeling of geometrical complexities followed bychallenging issues such as limitations in computational resources and almost unresolvabledifficulties in tracing the evolution of the modeled morphology during the loading.
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Title: Public Event Identification Traffic Data Using Machine Learning Approach
Creator: Yang, Hanyi
Date: 2020
Description: This study developed a shock waved diagram based deep learning model (SW-DLM) to predict the occurrence of public events in real-time...
Show moreThis study developed a shock waved diagram based deep learning model (SW-DLM) to predict the occurrence of public events in real-time according to their impacts on nearby highway traffic. Specifically, using point traffic volume data as a boundary condition, shock wave analysis is first conducted to understand the impacts and features of a public event on a nearby highway-ramp intersection. Next, this analysis develops the SWG algorithm to efficiently generate and expand shock wave diagrams in real-time according to the data collection rate. Built upon that, this study contributes a novel approach, which encodes a shock wave diagram with an optimal grid of pixels balancing resolution and computation load. Using the features extracted from encoded time-series shock wave diagrams as inputs, a deep learning approach, Long-short term memory (LSTM) model, is applied to predict the occurring of a public event. The numerical experiments based on the field data demonstrate that using encoded shock wave diagrams rather than point traffic data can significantly improve the accuracy of the deep learning for predicting the occurring of a public event. The SW-DLM presents satisfied prediction performance on the average as well as on an individual day with or without traffic accident interference, happening nearby the venue of a public event. The implementation of this approach to real-time traffic provision tools such as GPS will alert travelers en route on-going events in a transportation network and help travelers to make a smart trip plan and avoid traffic congestion. Moreover, it promotes smart city development by providing a strong capability to monitor the transportation system and conduct real-time traffic management intelligently.
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Title: OPTIMUM WEIGHT STIFFNESS STRUCTURAL DESIGN
Creator: Barnett, Ralph L.
Date: 2021
Description: My adventures with flexible structures began on the IIT campus with an extracurricular undergraduate project to design an “Open House Exhibit”...
Show moreMy adventures with flexible structures began on the IIT campus with an extracurricular undergraduate project to design an “Open House Exhibit” for the Civil Engineering Department. I chose to display a reinforced concrete diving board together with a prestressed concrete diving board. Visitors enthusiastically pounced on the reinforced concrete structure whose rigid response disappointed one and all. Their indignation was transferred to the prestressed cantilever which thrust them upward from six to ten feet into the air. This unexpected response from a diving board became so dangerous that the Exhibit was unceremoniously closed. I still have the display sign, “More Bounce to the Ounce.”While still an undergraduate, I secured a part-time job at Armour Research Foundation where I responded to a bid request from Rock Island Arsenal to design the 26 foot Honest John Rocket Launcher Rail at minimum weight. This tactical weapon was transported by helicopter. I basked in the fantasy that I was Leonardo da Vinci without his artistic proclivity. Rocket launchers that droop during operation are similar in concept to a circular firing squad. So began my research into minimum weight beams based on deflection rather than strength. I searched for the shoulders of Giants. I found them in the form of mathematicians not structural engineers. I achieved a 26.5% weight savings in the 1126 pound rail by optimizing the geometry. When I developed an optimum prestressed and segmented Kentanium cermet rail, the weight savings became 89%. The right material provides a bigger bang for the buck. When my journey into optimum design began, I was armed only with analysis tools: strength, stability, and stiffness. This thesis begins with an outline of my present toolbox which contains eight design concepts: 1. Establish the Geometry, 2. Select a material from a finite number of candidates, 3. Prestress and Prestrain, 4. Statistical Screening (Proof Testing), 5. Manipulation of Boundary Conditions, 6. Energized Systems, 7. Counterweights, 8. Self-Healing and Self-Reinforcing. Four of these are used through this review which focuses on stiffness. Beginning with beams, deflection control examples are described where prestraining and prestressing techniques are used to produce both a zero-deflection beam and a method for pushing with a chain. The calculus of variations made it possible to establish optimum tapers for the flanges and webs of I-beams that minimize beam weight for a specified deflection or, because of reciprocity, minimize beam deflection for a specified beam weight. An anomaly is encountered that enables one to achieve an upward, downward, or zero deflection with a set of beams of vanishing weight. In addition, special circumstances are defined where a uniform strength design is identical to the minimum weight design based on a specific deflection. Closed form solutions are obtained for a variety of loading scenarios. One problem is presented for self-weight that leads to a nonlinear integral equation. The optimum stiffness-weight design of trusses is undertaken where the area distribution of the truss members is optimized using Lagrange’s method of undetermined multipliers. Once again, we obtain a degenerate case where upward, downward, and zero deflection conditions can be met with an infinite set of trusses of vanishing weight. We photograph a simply supported truss under a downward load that leads to an upward deflection at one of the joints. Special loading conditions are identified that lead to uniform stress designs that are identical to the minimum weight designs based on deflections. This study provides a Segway into the world of minimum weight strength design of trusses. The resulting Maxwell and Michell trusses sometimes display the optimum distribution of bar areas from the point of view of stiffness. Many practitioners are under the mistaken impression that Michell structures, when they exist, provide the optimum truss profile for stiffness. Unfortunately, the optimum array of truss joints based on deflection does not exist. For both trusses and beams the optimum distribution of mass is shown to be necessary and sufficient; the sufficiency is established using well-known inequalities. The role of stiffness in the design of columns is explored in our final chapter. This cringe-worthy history of column analysis begins our study as a warning to practitioners who use analysis as their basis for design and especially optimum design. Conventional elastic and inelastic buckling theories provide little insight into the design of columns. The fundamentals of minimum weight column design are presented to show the power of design theory in contrast to analysis. Both prismatic and tapered columns are studied with one surprise result; the optimum taper gives rise to a uniform bending stress (without axial stresses). It was fun to see that in 1733 Lagrange made a mistake in calculus of variations that led to the incorrect solution for the optimum tapered column. It took 78 years before Clausen obtained the correct solution. The problem has been revisited by William Prager and again by the author who used dynamic programming. Of course, we all got the same result which is a dreadful solid circular tapered column that is heavier than any ordinary waterpipe. The best of a class is not necessarily the best possible design. Under the heading, “Intuition is a good servant but a bad master,” we introduce the notions of tension members that buckle, columns constructed from spherical beads, optimum rigging of crane booms, and deflection reversal of beam-columns. In several places we observe that the weight of optimum columns is proportional to P^α where P is the axial load and α is less than unity. We fail to tell the reader that this implies that minimum weight columns require putting all your eggs in one basket; one column under load P is lighter than two columns each under load P/2. On the other hand, we expose the solid circular column as the least efficient shape among all regular polygons, the equilateral triangle is the best. Indeed, there is a family of rectangles that are superior to the circular cross-section. Finally, the author’s prestressed tubular column is introduced that is pressurized to eliminate local buckling. Euler’s buckling can always be eliminated with a thin-wall section of sufficient width without a weight penalty. The weight of the balloon-like member is proportional to (PL) which implies that at last we have a compressive member that meets the requirement of a Michell structure. Bundling of pressurized gas columns are possible without a weight penalty. Further, the column is insensitive to most imperfections. It is the lightest known column for small structural indices (P/L^2 ). When coupled with circulating cryogenic liquid as a prestressing system, a limiting column has a vanishing weight.
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Title: INDUSTRIALIZED BUILDING CONSTRUCTION MODELS FOR TORNADO AFTERMATH RECOVERY
Creator: Alves de Carvalho, Augusto
Date: 2019
Description: Some researchers have reported that the number of disasters is expanding in scale and occurrences. Today, humanity occupies more land than...
Show moreSome researchers have reported that the number of disasters is expanding in scale and occurrences. Today, humanity occupies more land than forty years ago. Due to this, existing communities are prone to higher chances of being affected by disasters. Consequently, the number of natural disasters and losses have increased through time. Recent research work indicates that construction of new houses takes the majority of the recovery time; for example, In Joplin tornado aftermath, the development of new houses took the longest part of the recovery time (D. J. Smith & Sutter, 2013). The disaster industry sees housing and shelter as a product. The procurement is done on a necessity basis. The product --tents, inter-shelters, trailers, permanent dwellings, or any property to rent-- has to be ready whenever required. Therefore, after calculating the construction capacity in tornado regions, a methodology is proposed to compare four different robust industrialized building construction alternatives, keeping components, modules, and pieces in stock. Comparing them will provide information about which format is more appropriate for a profitable company or even a public entity, to respond and recover from a disaster faster.
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Title: A Risk-Based Approach in Selecting Design Natural Hazard Loads for Temporary Structures
Creator: Saleh, Eman
Date: 2020
Description: Temporary structures are systems that are used for short period applications such as in maintenance and retrofit applications or for staged...
Show moreTemporary structures are systems that are used for short period applications such as in maintenance and retrofit applications or for staged performances. Examples of its applications are tents, scaffoldings, and other facilities that have a short service life. Structures under construction and structures under serviceability conditions also fall under this category of structures; because their service time period is only limited to the duration of the construction, which is much shorter than the lifetime of the finished structure. One of the main characteristics of these types of structures is their high vulnerability to stability. Most specifications rarely cover temporary structures. Designing these structures to appropriate levels of the dead and live load does not impose an issue, in which using the same load factors as in permanent structures is considered a reasonable choice. However, an issue is raised when choosing the appropriate wind, seismic and snow load levels, where using the same exposure levels as in permanent structures may not be a desirable economic decision. Thus, for temporary structures, it makes sense to reduce the extreme event design loads proportional to the intended design life. In this manner, it is imperative to have specific rules or guidelines that would address the design aspects and reliability of these structures especially against lateral loads such as wind and earthquakes. This study aims at establishing several decision-making processes that could help contractors, designers, and erectors of temporary works to decide upon safety factors and/or return periods for environmental loads, with emphasis on the wind load. This decision-making process can be used in temporary projects (e.g., bridge erecting) to establish a design criterion based on the nature of the project. The study shows that the optimal decision-making process depends on the willingness to take advantage of wind locality characteristics (e.g., seasonality factor) in certain construction period or region, type of information available for the decision-maker (i.e., precise or imprecise), the risk associated with the constructed facility or the temporary structure itself, a potential for recourse actions, and the decision-maker’s attitude toward the trade-off between losses and gains with respect to uncertainty. The suggested decision-making process proposed is Bayesian decision process, the fuzzy decision process; (3) a two-stage stochastic programming solution; and (4) case-based decision theory. Several practical examples are presented in this thesis to show how different situations may require varying decision-making processes in order to reach the optimal decision. The design of temporary structures can be altered in response to a forecasted hurricane; thus, we propose a three-stage stochastic programming solution to decide upon their optimal wind design load. In addition, we extend the hurricane catastrophe models for application in temporary structures. This enables contractors to forecast the hurricane losses as a basis for estimating the adequate catastrophe cover such as insurance premiums and reinsurance for temporary structures. This scheme is then illustrated in an example for deciding the required temporary bracings for a steel frame under construction during the hurricane season.To prevent temporary structures from collapse, it is important to investigate the performance quality of previous projects and remove any causes for potential mishaps. This can be done by continuous monitoring of different projects and an investigation of accidents, if any, to help prevent future failures. In this study, we use an audit evidence scheme based on commonly available evidence theories used in the construction industry. In one such theory, the evidence is represented via a tree structure, in which the propagation is toward the variables that represent the project as a whole and separate work packages within a project. For simplicity, we only consider the binary case of variables i.e. whether or not a project conforms to the quality standards. The formulation of the auditing tool relates belief functions to the assertion of the quality assurance and quality control (QA/QC) measures and provides formulas for human error risk. These formulas provide plausibilities of human error in a belief-function format. An auditor may use the belief values to assess the degree of quality performance and to identify the sources of the problem in temporary work. We further illustrate the method in a practical application to evaluate the shoring/reshoring operations for estimating the construction risk in a multistory concrete structure. This evaluation may be used to decide on an appropriate time for formwork removal, shoring/reshoring schedule, casting cycles, post-tensioning sequence, and the required number of reshoring levels given the available evidence. To reduce the computational burden, we describe the shoring/reshoring system as a multi-state system (MSS) where the universal generating function (UGF) was used to estimate the reliability of the system.
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Title: OPTIMUM WEIGHT STIFFNESS STRUCTURAL DESIGN
Creator: Barnett, Ralph L.
Date: 2021
Description: My adventures with flexible structures began on the IIT campus with an extracurricular undergraduate project to design an “Open House Exhibit”...
Show moreMy adventures with flexible structures began on the IIT campus with an extracurricular undergraduate project to design an “Open House Exhibit” for the Civil Engineering Department. I chose to display a reinforced concrete diving board together with a prestressed concrete diving board. Visitors enthusiastically pounced on the reinforced concrete structure whose rigid response disappointed one and all. Their indignation was transferred to the prestressed cantilever which thrust them upward from six to ten feet into the air. This unexpected response from a diving board became so dangerous that the Exhibit was unceremoniously closed. I still have the display sign, “More Bounce to the Ounce.”While still an undergraduate, I secured a part-time job at Armour Research Foundation where I responded to a bid request from Rock Island Arsenal to design the 26 foot Honest John Rocket Launcher Rail at minimum weight. This tactical weapon was transported by helicopter. I basked in the fantasy that I was Leonardo da Vinci without his artistic proclivity. Rocket launchers that droop during operation are similar in concept to a circular firing squad. So began my research into minimum weight beams based on deflection rather than strength. I searched for the shoulders of Giants. I found them in the form of mathematicians not structural engineers. I achieved a 26.5% weight savings in the 1126 pound rail by optimizing the geometry. When I developed an optimum prestressed and segmented Kentanium cermet rail, the weight savings became 89%. The right material provides a bigger bang for the buck. When my journey into optimum design began, I was armed only with analysis tools: strength, stability, and stiffness. This thesis begins with an outline of my present toolbox which contains eight design concepts: 1. Establish the Geometry, 2. Select a material from a finite number of candidates, 3. Prestress and Prestrain, 4. Statistical Screening (Proof Testing), 5. Manipulation of Boundary Conditions, 6. Energized Systems, 7. Counterweights, 8. Self-Healing and Self-Reinforcing. Four of these are used through this review which focuses on stiffness. Beginning with beams, deflection control examples are described where prestraining and prestressing techniques are used to produce both a zero-deflection beam and a method for pushing with a chain. The calculus of variations made it possible to establish optimum tapers for the flanges and webs of I-beams that minimize beam weight for a specified deflection or, because of reciprocity, minimize beam deflection for a specified beam weight. An anomaly is encountered that enables one to achieve an upward, downward, or zero deflection with a set of beams of vanishing weight. In addition, special circumstances are defined where a uniform strength design is identical to the minimum weight design based on a specific deflection. Closed form solutions are obtained for a variety of loading scenarios. One problem is presented for self-weight that leads to a nonlinear integral equation. The optimum stiffness-weight design of trusses is undertaken where the area distribution of the truss members is optimized using Lagrange’s method of undetermined multipliers. Once again, we obtain a degenerate case where upward, downward, and zero deflection conditions can be met with an infinite set of trusses of vanishing weight. We photograph a simply supported truss under a downward load that leads to an upward deflection at one of the joints. Special loading conditions are identified that lead to uniform stress designs that are identical to the minimum weight designs based on deflections. This study provides a Segway into the world of minimum weight strength design of trusses. The resulting Maxwell and Michell trusses sometimes display the optimum distribution of bar areas from the point of view of stiffness. Many practitioners are under the mistaken impression that Michell structures, when they exist, provide the optimum truss profile for stiffness. Unfortunately, the optimum array of truss joints based on deflection does not exist. For both trusses and beams the optimum distribution of mass is shown to be necessary and sufficient; the sufficiency is established using well-known inequalities. The role of stiffness in the design of columns is explored in our final chapter. This cringe-worthy history of column analysis begins our study as a warning to practitioners who use analysis as their basis for design and especially optimum design. Conventional elastic and inelastic buckling theories provide little insight into the design of columns. The fundamentals of minimum weight column design are presented to show the power of design theory in contrast to analysis. Both prismatic and tapered columns are studied with one surprise result; the optimum taper gives rise to a uniform bending stress (without axial stresses). It was fun to see that in 1733 Lagrange made a mistake in calculus of variations that led to the incorrect solution for the optimum tapered column. It took 78 years before Clausen obtained the correct solution. The problem has been revisited by William Prager and again by the author who used dynamic programming. Of course, we all got the same result which is a dreadful solid circular tapered column that is heavier than any ordinary waterpipe. The best of a class is not necessarily the best possible design. Under the heading, “Intuition is a good servant but a bad master,” we introduce the notions of tension members that buckle, columns constructed from spherical beads, optimum rigging of crane booms, and deflection reversal of beam-columns. In several places we observe that the weight of optimum columns is proportional to P^α where P is the axial load and α is less than unity. We fail to tell the reader that this implies that minimum weight columns require putting all your eggs in one basket; one column under load P is lighter than two columns each under load P/2. On the other hand, we expose the solid circular column as the least efficient shape among all regular polygons, the equilateral triangle is the best. Indeed, there is a family of rectangles that are superior to the circular cross-section. Finally, the author’s prestressed tubular column is introduced that is pressurized to eliminate local buckling. Euler’s buckling can always be eliminated with a thin-wall section of sufficient width without a weight penalty. The weight of the balloon-like member is proportional to (PL) which implies that at last we have a compressive member that meets the requirement of a Michell structure. Bundling of pressurized gas columns are possible without a weight penalty. Further, the column is insensitive to most imperfections. It is the lightest known column for small structural indices (P/L^2 ). When coupled with circulating cryogenic liquid as a prestressing system, a limiting column has a vanishing weight.
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Title: Influence Of Internal Factors In Construction Organizations On The Implementation Of Integrated Project Delivery Viewed From The Organizational Change Theory
Creator: Rashed, Ahmed
Date: 2022
Description: Integrated Project Delivery (IPD) is an emerging construction project delivery system that is collaborative oriented. It involves the critical...
Show moreIntegrated Project Delivery (IPD) is an emerging construction project delivery system that is collaborative oriented. It involves the critical participants in an early stage of the project timeline. Recently, IPD is becoming increasingly common. Many organizations are interested in contributing to the Architecture, Engineering, and Construction (AEC) industry. No research studies have previously observed and studied the effect of IPD implementation through an organizational change theory lens. The presented research work was designed to explore the role of organizational factors in the implementing first domain, reflecting the organizational level factors, including cultural and economic considerations. In contrast, the second domain focuses on member-level factors, i.e., employee involvement and readiness to change. Together, these domains influence the organization’s intention and adoption to change toward the IPD as a project delivery system. This impact is viewed through the lens of the OCT based on the contributions and theories discussed by various researchers. These researchers are from a variety of disciplines. A data collection survey was developed to gather quantitative data from the industry. Data was collected from N=128 employees from the construction industry. Data analysis was performed through Structure Equation Modeling using Smart PLS 3. Results showed that communication, integration significantly associated IPD implementation. Moreover, involvement and readiness change also positively predicted the implementation of IPD. The empirical result of current study validates all the constructs of the hypothetical model except reward system.
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Title: Fatigue Life Prediction for Structures with Interval Uncertainty
Creator: Desch, Michael R.
Date: 2022
Description: A new method for reliable fatigue life prediction in metal structural components is developed where uncertainties are quantified using...
Show moreA new method for reliable fatigue life prediction in metal structural components is developed where uncertainties are quantified using interval variables. Using this crack-initiation-based method, first, the uncertainties in laboratory test data for the fatigue failure of a structural detail are enumerated. This uncertainty quantification is performed through an interval-based enveloping procedure that relates the interval stress ranges to the number of cycles to failure, leading to the construction of an interval S-N relationship. Next, the uncertainties in field test data are enumerated in the extremum values of each stress range, as intervals, leading to the construction of interval stress ranges. For both the laboratory and field data uncertainty analyses, the mean stress effects are considered. Next, the interval damage accumulated over the duration of the field data is determined using the constructed interval S-N relationship and the obtained interval stress ranges. Then, the interval existing damage and interval remaining life are determined. Finally, as a conservative measure, the minimum remaining fatigue life is obtained in which all uncertainties are considered. Three numerical examples illustrating the developed method are presented, and the results are compared with results obtained by both Monte Carlo simulation and optimization. Using this method, for the numerical examples considered, it is shown that the results for bounds on the existing damage and the remaining fatigue life are sharp. Moreover, due to its set-based approach, the method is significantly more computationally efficient when compared with iterative procedures.
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Title: INTEGRATED DECISION SUPPORT SYSTEM FOR THE SELECTION AND IMPLEMENTATION OF DELAY ANALYSIS IN CONSTRUCTION PROJECTS
Creator: Yang, Juneseok
Date: 2022
Description: The goal of this study is to establish an objective, user-friendly, and reliable decision support system, called delay analysis selection and...
Show moreThe goal of this study is to establish an objective, user-friendly, and reliable decision support system, called delay analysis selection and implementation system (DASIS), which allows delay analysts and practitioners in the construction industry to select a type of delay analysis that is most appropriate for given conditions and to perform the selected type of delay analysis. DASIS integrates a delay analysis selection system (DASS) module and an implementation module (DAIS) that performs the type of delay analysis selected by DASS in construction projects.The model that operates the DASS module consists of (1) four different delay analysis approaches currently available to practitioners; (2) a set of 26 attributes that affect the selection of a type of delay analysis; (3) a case-base involving 3,776 cases described by these 26 attributes and their corresponding output values (i.e., the most appropriate delay analysis approach); (4) a set of 7 categories consisting of subsets of attributes; (5) the weights of the attributes and the categories; and (6) a spreadsheet designed in Microsoft Excel that performs the calculations involved in case-based similarity assessment. The implementation module is a computerized analytics and automation platform that performs the type of delay analysis selected by DASS. In developing the DASS module, 26 attributes that influence the selection of the most appropriate type of delay analysis were identified based on a thorough literature review and were organized in seven categories. These attributes were used to evaluate the four types of delay analysis (i.e., static, dynamic, additive, and subtractive analyses). Based on the results of this evaluation, a case-base of 3,776 cases was generated while considering the constraints of each category. The weights of the attributes and categories were determined by using several methods. To determine the best-fit between a target case (defined by its 26 attributes) and the 3,776 cases stored in the case-base were used to perform a case-based similarity assessment to calculate weighted case similarity scores, and to find the best-informed solution to the delay analysis type selection problem. In developing the DAIS module, the four types of delay analysis were coded in Microsoft Excel using macros programmed in Visual Basic for Applications (VBA). This automated tool performs the selected delay analysis by DASS. The fully integrated DASIS model finds the best-fit match between a target case and cases stored in the case-base by means of similarity assessment methods by using weighted case similarity scores, hence identifying the most appropriate type of delay analysis for use in the target case, performs the selected type of delay analysis and generates a report about the results of the delay analysis to the analyst instantaneously, allowing the contractual parties to settle the issues quickly. This study is the first attempt to establish an objective decision support system (DASS) to assist delay analysts by automating the selection of a type of delay analysis using combinations of well recognized and reliable attributes and similarity assessment techniques. In addition, DASS is immediately followed by DAIS in an integrated system (DASIS) that does not only do the selection of the most appropriate type of delay analysis, but that also implements the selected delay analysis, hence providing ease of use and high speed. A case study based on fictitious scenarios is presented to demonstrate and validate the research approach. The use of the entropy weight method to calculate the weights of the attributes can be considered a minor limitation of the study. Finally, DASIS can be reformulated as a web-based application that allows analysts to work online using ordinary browsers anywhere and anytime.
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Title: Evaluation of Bridge Abutment Slope Protection at Stream Crossings
Creator: Wang, Peng
Date: 2023
Description: Extensive research has revealed that scour and flooding contribute to over 50% of bridge failures in the United States, with scour-induced...
Show moreExtensive research has revealed that scour and flooding contribute to over 50% of bridge failures in the United States, with scour-induced failures alone causing the collapse of 20-100 over-water bridges annually out of a total population of approximately 504,000 bridges. Within Wisconsin, a significant number of bridges, specifically over 1200, have been identified as scour-critical, with 200 of them experiencing slope instability issues.This study focuses on the problematic bridge sites in Wisconsin, particularly examining the underperformance of abutment slopes. To identify and document these problematic bridges, a comprehensive survey was conducted, followed by site visits. Subsequently, a thorough Limit Equilibrium Method (LEM) simulation was carried out based on an investigated bridge. The simulation results indicate that the infiltration of water into the slope berm areas significantly decreases slope stability due to seepage forces. Furthermore, the absence of riprap toe protection can result in overall slope failure. The implementation of concrete pouring to address riprap scoring has proven unreliable, leading to frequent failures.Additionally, simulations were performed for grouted riprap, slope walls, grouted tiebacks, and piles. The results demonstrate their potential to enhance slope safety, with their suitability requiring careful evaluation. Notably, a simulation comparing a 1:2 slope design with a 1:1.5 slope inclination reveals that the former significantly improves slope safety.In Chapter 5, a comprehensive life cycle cost analysis is conducted, comparing the 1:2 slope design to the 1:1.5 design. The analysis reveals that the 1:2 design method is more cost-effective over a 60-year study period.In conclusion, this research provides valuable insights into the assessment and mitigation of abutment slope protection issues in Wisconsin. The findings emphasize the importance of considering seepage forces, appropriate riprap installation, and alternative stabilization measures together with a comprehensive life cycle cost analysis. The research contributes to enhancing slope safety and informs decision-making processes for bridge design and maintenance.
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